parse.rs

trait FromValue<T> {
    fn from_value(edn::Value) -> Option<T>;
}

impl FromValue<PatternNonValuePlace> for PatternNonValuePlace {
    fn from_value(v: edn::Value) -> Option<PatternNonValuePlace> {
        match v {
            edn::Value::Integer(x) => if x >= 0 {
                Some(PatternNonValuePlace::Entid(x as u64))
            } else {
                None
            },
            edn::Value::PlainSymbol(x) => if x.0.as_str() == "_" {
                Some(PatternNonValuePlace::Placeholder)
            } else if x.is_var_symbol() {
                Some(PatternNonValuePlace::Variable(Variable(x)))
            } else {
                None
            },
            edn::Value::NamespacedKeyword(x) =>
                Some(PatternNonValuePlace::Ident(x)),
            _ => None,
        }
    }
}

…

    fn pattern_non_value_place() -> ResultParser<PatternNonValuePlace, I> {
        fn_parser(Where::<I>::pattern_non_value_place_, "pattern_non_value_place")
    }

    fn pattern_non_value_place_(input: I) -> ParseResult<PatternNonValuePlace, I> {
        satisfy_map(|x: edn::Value| PatternNonValuePlace::from_value(x)).parse_stream(input)
    }